Thin-film transistor, method of manufacturing the same, and method of manufacturing backplane for flat panel display

ABSTRACT

Provided are a thin-film transistor (TFT), a method of manufacturing the same, and a method of manufacturing a backplane for a flat panel display (FPD). The method of manufacturing the TFT according to an embodiment of the present invention includes forming a gate electrode on a substrate; forming an insulating layer on the substrate to cover the gate electrode; performing a plasma treatment on an upper surface of the insulating layer using a halogen gas; forming an oxide semiconductor layer on the insulating layer and positioned to correspond to the gate electrode; and forming source and drain electrodes on the insulating layer to contact and over portions of the oxide semiconductor layer.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/339,232 filed on Jul. 23, 2014, which claimspriority to Korean Patent Application No. 10-2013-0088971, filed on Jul.26, 2013 in the Korean Intellectual Property Office, the disclosures ofwhich are incorporated herein by reference in their entirety.

BACKGROUND

1. Field

One or more embodiments of the present invention relate generally toflat panel displays. More specifically, one or more embodiments relateto a thin-film transistor, a method of manufacturing the same, and amethod of manufacturing a backplane for a flat panel display.

2. Description of the Related Art

In recent years, as interest in information displays and demand forportable information media increase, research and commercialization hascentered on light and thin flat panel displays (FPDs) that are replacingcathode ray tubes (CRTs) as commonly accepted display devices.

Since organic light-emitting displays (OLEDs), one type of FPDs, areself-luminous type FPDs, OLEDs tend to have good viewing angle andcontrast ratio, as compared to liquid crystal displays (LCDs). Also,OLEDs do not need a backlight, and thus may be light and thin ascompared to LCDs. OLEDs are also advantageous in terms of powerconsumption. Furthermore, OLEDs are advantageous in that they may bedriven with a direct-current low voltage, and have high response rates.OLEDs are also advantageous in terms of manufacturing costs.

Recent efforts have focused on enlarging the display area of OLEDs. Tothis end, it is necessary to develop, as driving transistors for theOLED, thin-film transistors (TFTs) which have constant currentcharacteristics, to ensure stable operation and durability. Oxidesemiconductors have a higher mobility than silicon semiconductors, andTFTs using oxide semiconductors are thus being increasingly utilized.

SUMMARY

One or more embodiments of the present invention provide a thin-filmtransistor including an oxide semiconductor, and a method ofmanufacturing the same.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to one or more embodiments of the present invention, a methodof manufacturing a thin-film transistor (TFT) includes: forming a gateelectrode on a substrate; forming an insulating layer on the substrateto cover the gate electrode; performing a plasma treatment on an uppersurface of the insulating layer, the plasma treatment using a halogengas; forming an oxide semiconductor layer on the insulating layer andpositioned to correspond to the gate electrode; and forming source anddrain electrodes on the first insulating layer and over portions of theoxide semiconductor layer.

The halogen gas may include nitrogen fluoride (NF₃).

The insulating layer may include a high dielectric oxide film.

The insulating layer may include hafnium oxide (HfO_(x)).

The forming an insulating layer may include forming the first insulatinglayer by a sol-gel process.

The forming an insulating layer may further comprise performing thesol-gel process using a solution comprising hafnium chloride (HfCl₄)dissolved in a solvent that includes at least one of acetonitrile andethylene glycol.

The method may further include annealing the insulating layer.

The oxide semiconductor layer may include an amorphous metal oxide.

The oxide semiconductor layer may include a zinc-tin oxide (ZTO).

The forming an oxide semiconductor layer may include forming the oxidesemiconductor layer by spin coating or inkjet printing.

According to one or more embodiments of the present invention, athin-film transistor (TFT) includes: a substrate; a gate electrodedisposed on the substrate; an insulating layer disposed on the substrateto cover the gate electrode, the insulating layer having an uppersurface that has been plasma-treated using a halogen gas; an oxidesemiconductor layer disposed on the insulating layer and positioned tocorrespond to the gate electrode; and source and drain electrodesdisposed on the insulating layer and over portions of the oxidesemiconductor layer.

The halogen gas may include nitrogen fluoride (NF₃).

The insulating layer may include a high dielectric oxide film.

The insulating layer may include a hafnium oxide.

The oxide semiconductor layer may include an amorphous metal oxide.

The oxide semiconductor layer may include a zinc-tin oxide.

According to one or more embodiments of the present invention, a methodof manufacturing a backplane for a flat panel display (FPD) includes:forming a gate electrode on a substrate; forming a first insulatinglayer on the substrate to cover the gate electrode; performing a plasmatreatment on an upper surface of the first insulating layer, the plasmatreatment using a halogen gas; forming an oxide semiconductor layer onthe first insulating layer and positioned to correspond to the gateelectrode; forming source and drain electrodes on the first insulatinglayer and over portions of the oxide semiconductor layer; forming asecond insulating layer on the first insulating layer to cover thesemiconductor layer and the source and drain electrodes, the secondinsulating layer including a first hole exposing the source and drainelectrodes; and forming a pixel electrode on the second insulating layerand within the first hole.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view illustrating an oxidethin-film transistor (TFT) according to an embodiment of the presentinvention;

FIG. 2 is a schematic cross-sectional view illustrating a backplane fora flat panel display (FPD), according to an embodiment of the presentinvention;

FIGS. 3 to 8 are schematic cross-sectional views illustrating amanufacturing method of an oxide TFT, according to an embodiment of thepresent invention;

FIGS. 9 and 10 are graphs illustrating a sputtering depth profile ofzinc (Zn); and

FIGS. 11 and 12 are graphs illustrating a voltage-current characteristicof the oxide TFT.

The various figures are not necessarily to scale.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

Since the present disclosure may have diverse modified embodiments,exemplary embodiments are illustrated in the drawings and are describedin the detailed description of the invention. However, this does notlimit the present disclosure within specific embodiments and it shouldbe understood that the present disclosure covers all the modifications,equivalents, and replacements within the idea and technical scope of thepresent disclosure. Detailed descriptions related to well-knownfunctions or configurations will be ruled out in order to clearlyexplain with respect to features of the embodiments of the presentinvention.

In the following description, the technical terms are used only forexplain a specific exemplary embodiment while not limiting the presentdisclosure. The terms of a singular form may include plural forms unlessreferred to the context. The meaning of “include”, “comprise”, “have”,“including”, “comprising”, or “having” specifies a property, a region, afixed number, a step, a process, an element, a component and/or acombination of relevant constituent elements but does not exclude otherproperties, regions, fixed numbers, steps, processes, elements acomponent and/or a combination of relevant constituent elements.

It will be understood that although the terms “first”, “second” and thelike are used herein to describe various elements, these elements shouldnot be limited by these terms. Terms such as these are only used todistinguish one component or element from other components or elements.

It will also be understood that when a layer (or film), a region, or acomponent is referred to as being cony another element, it can bedirectly on the other element, or intervening layers, regions, orcomponents may also be present.

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view illustrating an oxidethin-film transistor (TFT) according to an embodiment of the presentinvention. Referring to FIG. 1, the oxide TFT according to thisembodiment of the present invention includes a substrate 10, a gateelectrode 11 disposed on the substrate 10, a first insulating layer 12which is disposed on the substrate 10 to cover the gate electrode 11 andof which an upper surface 12-1 is plasma-treated by using a halogen gas,an oxide semiconductor layer 13 disposed on the first insulating layer12 to face the gate electrode 11, and a source electrode 14 a and adrain electrode 14 b disposed on the first insulating layer 12 tocontact portions of the oxide semiconductor layer 13.

FIG. 2 is a schematic cross-sectional view illustrating a backplane fora flat panel display (FPD) according to an embodiment of the presentinvention. Referring to FIG. 2, the backplane for an FPD according to anembodiment of the present invention includes the oxide TFT illustratedin FIG. 1; a second insulating layer 15 disposed on the first insulatinglayer 12 to cover the oxide semiconductor layer 13 as well as the sourceand drain electrodes 14 a and 14 b, the second insulating layer 15including a hole exposing the source electrode 14 a or the drainelectrode 14 b; and a pixel electrode 16 disposed on the secondinsulating layer 15 and within the hole in the second insulating layer15.

Referring to FIG. 2, the backplane for the FPD, according to thisembodiment of the present invention, further includes a third insulatinglayer 17 disposed on the second insulating layer 15 to cover an edge ofthe pixel electrode 16, an intermediate layer 18 including an emissionlayer and being disposed on that portion of the pixel electrode 16 whichis exposed by an opening in the third insulating layer 17, and anopposite electrode 19 facing the pixel electrode 16 with theintermediate layer 18 interposed therebetween.

FIGS. 3 to 8 are schematic cross-sectional views illustrating amanufacturing method for the oxide TFT of embodiments of the presentinvention.

First, as illustrated in FIG. 3, a substrate 10 is provided. Thesubstrate 10 may be formed of a transparent glass material mainlycomposed of SiO₂. However, the substrate 10 is not limited thereto, andthus the substrate 10 may be formed from various other materials such asan opaque material, a plastic material, or a metal material.

An auxiliary layer (not shown), such as a barrier layer, a blockinglayer, and/or a buffer layer, may be provided on the substrate 10 so asto prevent impurity ions from diffusing through the substrate 10 andwater or ambient air from infiltrating thereinto, as well as toplanarize the surface of the substrate 10. The auxiliary layer may beformed using SiO₂ and/or SiN_(x) through various deposition methods,such as plasma-enhanced chemical vapor deposition (PECVD), atmosphericpressure CVD (APCVD), and low pressure CVD (LPCVD). The auxiliary layer,however, may be omitted.

Referring to FIG. 4, a gate electrode 11 is formed on the substrate 10.To form the gate electrode 11, a metal layer may be laminated on thesubstrate 10 and then selectively etched. However, formation of the gateelectrode 11 is not limited to this method. For example, the gateelectrode 11 may alternatively be formed by patterning through a maskingprocess which uses a lift-off process.

The gate electrode 11 may be formed of a conductive material. Forexample, the gate electrode 11 may include at least one materialselected from silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt),palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir),chromium (Cr), lithium (Li), calcium (Ca), molybdenum (Mo), titanium(Ti), tungsten (W), molybdenum-tungsten (MoW), and copper (Cu). However,the material of the gate electrode 11 is not limited thereto, and thusthe gate electrode 11 may be formed of any conductive material, such asthat containing metal, or the like.

As illustrated in FIG. 5, a first insulating layer 12 is formed on thesubstrate 10 to cover the gate electrode 11. The first insulating layer12 may function as a gate insulating layer disposed between the gateelectrode 11 and an oxide semiconductor layer 13 (that will be describedlater) to insulate the gate electrode 11 from the oxide semiconductorlayer 13.

The first insulating layer 12 may be formed by various processes such asa chemical vapor deposition method like CVD or PECVD, by a physicalvapor deposition (PVD) method such as sputtering, or by a sol-gelprocess such as spin coating or inkjet printing.

The first insulating layer 12 may be formed of an inorganic substance,such as silicon oxide or silicon nitrogen. However, the first insulatinglayer 12 may include a high dielectric oxide film such as a hafniumoxide or an aluminum oxide. For example, the hafnium oxide may includeHfAlO, HfLaO, HfO₂, HfON, HfSiO, or HfSiON.

For example, the first insulating layer 12 may be formed by a sol-gelprocess so that the first insulating layer 12 includes theabove-described hafnium oxide. For example, the first insulating layer12 may be formed by a sol-gel process using a solution in which hafniumchloride (HfCl₄) is dissolved in a solvent including at least one ofacetonitrile and ethylene glycol.

As illustrated in FIG. 5, an upper surface of the first insulating layer12 is plasma-treated using a halogen gas.

As illustrated in FIG. 6, the surface treatment layer 12-1 may be formedon an upper surface of the first insulating layer 12 by plasmatreatment. When the oxide semiconductor layer 13 (that will be describedbelow) is formed, components of the oxide semiconductor layer 13 mayinfiltrate into the first insulating layer 12. However, the surfacetreatment layer 12-1 may prevent these components from infiltrating ordiffusing into the first insulating layer 12. Therefore, the oxide TFTmay retain its superior characteristics. Also, such effects will bedescribed with reference to FIGS. 9 and 12.

When the insulating layer is plasma-treated using a halogen gas, thehalogen gas may include a halogen material. For example, the halogen gasmay include nitrogen fluoride (NF₃). However, NF₃ is but one example ofthe halogen material, and the composition of the halogen gas is notlimited thereto.

An annealing process for the first insulating layer 12 may be furtherperformed according to an embodiment of the present invention. Forexample, the first insulating layer 12 may be annealed at a temperatureranging between about 100° C. and about 300° C.

As illustrated in FIG. 7, the oxide semiconductor layer 13 may be formedon the first insulating layer 12 to face the gate electrode 11. Theoxide semiconductor layer 13 may be positioned so as to face (i.e.,positioned over, or overlapping) the gate electrode 11 with theinsulating layer 12 disposed therebetween.

The oxide semiconductor layer 13 may include an amorphous metal oxide.For example, the oxide semiconductor layer 13 may include oxide materialselected from metal elements of Groups 12, 13, and 14, such as Zn, In,gallium (Ga), tin (Sn), cadmium (Cd), germanium (Ge), or Hf, and/or anycombination thereof. However, this is merely an example, and thus amaterial of the oxide semiconductor layer 13 is not limited thereto. Forexample, the oxide semiconductor layer 13 may include zinc-tin oxide(ZTO).

The oxide semiconductor layer 13 may be formed by a sol-gel process. Forexample, the oxide semiconductor layer 13 may be formed by spin coatingor inkjet printing.

Referring to FIG. 8, source and drain electrodes 14 a and 14 b areformed on the first insulating layer 12 to contact a portion of theoxide semiconductor layer 13. In detail, the source and drain electrodes14 a and 14 b may be formed on the surface treatment layer 12-1 that isformed on the first insulating layer 12, to partially overlap both theoxide semiconductor layer 13 and the surface treatment layer 12-1.

Referring to FIG. 8, a top surface of the oxide semiconductor layer 13is not fully covered by the source and drain electrodes 14 a and 14 b,and the source and drain electrodes 14 a and 14 b are spaced apart fromeach other.

A metal layer may be laminated on the structure illustrated in FIG. 5and then selectively etched in order to form the source and drainelectrodes 14 a and 14 b. The etching process may include variousprocesses, such as wet etching and dry etching. The metal layer mayinclude at least one material selected from silver (Ag), magnesium (Mg),aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni),neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca),molybdenum (Mo), titanium (Ti), tungsten (W), molybdenum-tungsten (MoW),and copper (Cu). However, materials of the source and drain electrodes14 a and 14 b are not limited thereto, and thus the source and drainelectrodes 14 a and 14 b may be formed of any conductive material, suchas that containing metal, or the like.

For example, the source and drain electrodes 14 a and 14 b may use atransparent conductive material or a conductive polymer such as anindium tin oxide (ITO) and an indium zinc oxide (IZO), and may have amulti-layered structure in which at least two conductive materials arelaminated.

However, a method of forming the source and drain electrodes 14 a and 14b will not be limited thereto. For example, the source and drainelectrodes 14 a and 14 b may be patterned by a masking process whichuses a lift-off process.

Although not shown, an additional insulating layer may be disposedbetween the oxide semiconductor layer 13 and the source and drainelectrodes 14 a and 14 b.

By forming a second insulating layer 15, a pixel electrode 16, a thirdinsulating layer 17, an intermediate layer 18, and an opposite electrode19 on the structure of FIG. 8 in sequence, a backplane of a flat paneldisplay (FPD) as illustrated in FIG. 2 may be obtained. The method offorming the above configuration on the structure of FIG. 8 to form thestructure of FIG. 2 is as follows:

First, the second insulating layer 15 may be formed on the firstinsulating layer 12 to cover the oxide semiconductor layer 13 and thesource and drain electrodes 14 a and 14 b. A first hole is then formedin the second insulating layer 15, by which the source and/or drainelectrodes 14 a and 14 b are exposed. In detail, the second insulatinglayer 15 may be formed on the surface treatment layer 12-1 of the firstinsulating layer 12.

Thereafter, the pixel electrode 16 may be formed on the secondinsulating layer 15 and thus fill the first hole of the secondinsulating layer 15. The pixel electrode 16 may be in contact with thesource and drain electrodes 14 a and 14 b through the first hole of thesecond insulating layer 15.

Afterwards, the third insulating layer 17 may be formed on the secondinsulating layer 15 to cover an edge of the pixel electrode 16, and mayinclude an opening exposing at least one portion of the pixel electrode16.

Then, the intermediate layer 18 having an emission layer may be formedon the portion of the pixel electrode 16 exposed by the opening. Theopposite electrode 19 may be formed to face the pixel electrode 16, withthe intermediate layer 18 interposed therebetween.

The second and third insulating layers 15 and 17 may be formed by asol-gel process.

Referring to FIG. 2, the organic light-emitting diode may be providedwith the pixel electrode 16, the intermediate layer 18, and the oppositeelectrode 19. Thus, a backplane for a flat panel display manufacturedaccording to the embodiments of the present invention may be used as abackplane for the organic light-emitting display (OLED). However, theembodiments of the present invention are not limited to theconfiguration shown. For example, if liquid crystal is disposed betweenthe pixel electrode 16 and the opposite electrode 19, the backplane forthe flat panel display manufactured according to the embodiments of thepresent invention may be used as a backplane for a liquid crystaldisplay.

FIGS. 9 and 10 are graphs illustrating a sputtering depth profile ofzinc, from which a change in zinc concentration depending on a depthfrom the target surface may be observed through the relationship of zincconcentration versus a sputtering time, when zinc is supplied to thetarget by a sputtering method. In detail, FIGS. 9 and 10 are graphsillustrating a sputtering depth profile of zinc in the substrate 10 onwhich the oxide semiconductor layer 13 is formed. In particular, FIGS. 9and 10 are graphs illustrating a sputtering depth profile of a zinccomponent, when the oxide semiconductor layer 13 is formed of ZTO.

In detail, FIG. 9 illustrates an example in which the oxidesemiconductor layer 13 is formed on the first insulating layer 12without performing a plasma treatment on the upper surface of the firstinsulating layer 12. FIG. 10 illustrates an example in which the uppersurface of the first insulating layer 12 is plasma-treated using ahalogen material, for example NF₃, to form the surface treatment layer12-1, and then the oxide semiconductor layer 13 is formed on the surfacetreatment layer 12-1.

In FIGS. 9 and 10, the abscissa axis in the graph represents a timespent in performing sputtering of the oxide semiconductor layer 13 uponthe first insulating layer 12. In the sputtering depth profile graph,the sputtering time is proportional to a depth from the surface of thetarget, as the thickness of oxide semiconductor layer 13 continuallyincreases during sputtering. Therefore, the sputtering time isproportional to a depth from the oxide semiconductor layer 13 in FIGS. 9and 10. In FIGS. 9 and 10, the ordinate axis in the graph represents thepercentage of zinc atoms with respect to all the atoms.

In the depth profile graph as illustrated in FIGS. 9 and 10, ifcomponent concentration sharply changes, it may mean that there is aninterface between two layers. In FIGS. 9 and 10, an area where the zincconcentration sharply decreases may be considered as an interfacebetween the oxide semiconductor layer 13 and the first insulating layer12.

In comparing the graphs of FIGS. 9 and 10, the slope of zincconcentration at the interface between the oxide semiconductor layer 13and the first insulating layer 12 is steeper in the graph of FIG. 10than in the graph of FIG. 9. That is, in FIG. 10, zinc penetrates lessinto the first insulating layer 12 due to the surface treatment layer12-1 formed by performing a plasma treatment on the upper surface of thefirst insulating layer 12.

FIGS. 11 and 12 are graphs illustrating voltage-current characteristicsof an oxide TFT constructed according to embodiments of the invention.In detail, FIG. 11 is a graph illustrating the voltage-currentcharacteristics of the oxide TFT which is formed on the first insulatinglayer 12 without performing a plasma treatment on the upper surface ofthe first insulating layer 12. FIG. 12 is a graph illustrating thevoltage-current characteristics of the oxide TFT in which the uppersurface of the first insulating layer 12 is plasma-treated using ahalogen material to form the surface treatment layer 12-1.

A plurality of curves in FIGS. 11 and 12 represent voltage-currentcharacteristics measured under environments with different biasvoltages. Referring to FIGS. 11 and 12, the voltage-currentcharacteristic of the oxide TFT slightly shifts according to changes inbias voltage in FIG. 11. On the contrary, in FIG. 12, thevoltage-current characteristic of the device is relatively stablymaintained, even if the bias voltage changes. Also, the voltage-currentcharacteristic at a threshold voltage illustrated in FIG. 12 is superiorto that in FIG. 11.

That is, the upper surface of the first insulating layer 12 isplasma-treated to form the surface treatment layer 12-1 to haveexcellent interface characteristics between the oxide semiconductorlayer 13 and the first insulating layer 12, thereby improving devicecharacteristics.

A masking process performed to form a backplane for the oxide TFT andthe FPD as described above may be performed by dry etching or wetetching. Also, although only one transistor is illustrated in thefigures for explaining the backplane for the FPD according toembodiments of the present invention for convenience of description, theembodiments of the present invention are not limited thereto. Forexample, the backplane for the FPD according to embodiments of thepresent invention may include a plurality of transistors unless thenumber of masking processes according to the embodiment of the presentinvention increases.

As described above, according to the one or more of the aboveembodiments of the present invention, it is possible to provide an oxideTFT having more stable device characteristics.

While various embodiments of the present invention have beenparticularly shown and described with reference to exemplary embodimentsthereof, it will be that various changes in form and details may be madetherein without departing from the spirit and scope of the embodimentsof the present invention as defined by the following claims.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only, and not for purposesof limitation. Descriptions of features or aspects within eachembodiment should typically be considered as available for other similarfeatures or aspects in other embodiments. That is, various features ofthe various embodiments described can be mixed and matched to form otherembodiments.

While one or more embodiments of the present invention have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of theembodiments of the present invention as defined by the following claims.

What is claimed is:
 1. A thin-film transistor (TFT) comprising: asubstrate; a gate electrode disposed over the substrate; an insulatinglayer disposed over the substrate to cover the gate electrode; a surfacetreatment layer on an upper surface of the insulating layer, the surfacetreatment layer comprising nitrogen fluoride (NF₃); an oxidesemiconductor layer disposed on the surface treatment layer andpositioned to correspond to the gate electrode; and source and drainelectrodes disposed on the surface treatment layer and portions of theoxide semiconductor layer.
 2. The TFT of claim 1, wherein the insulatinglayer comprises a high dielectric oxide film.
 3. The TFT of claim 3,wherein the insulating layer comprises a hafnium oxide.
 4. The TFT ofclaim 1, wherein the oxide semiconductor layer comprises an amorphousmetal oxide.
 5. The TFT of claim 1, wherein the oxide semiconductorlayer comprises zinc-tin oxide.